Don’t look at the leader board too often. Don’t wonder: “What will it take to win this miserable, magnificent U.S. Open? Even par? Three under par? What’s everybody else doing? Collapsing? Charging? Is this one of those years when 5 over wins and if I just stop gagging my guts out I’ll win?”

At the U.S. Open, you absolutely never know what it will take to prevail. And if you think about it, you are automatically and invariably dead.

It you make three straight bogeys and all those familiar black-dog golf thoughts invade your soul and you think (even though you know you shouldn’t), “I’ve let my Open chance slip away,” then that thought itself — far more than those bogeys — becomes a self-fulfilling prophecy.

“We’re all scared of messing up. We all have a fear of success or a fear of failure. I only have fear of failure,” said the 2010 champion at Pebble Beach, who says the Pacific sea air reminds him of his homeland. “I was nervous, anxious before the round. I had to get my head screwed back on right.”

On this glistening day, he did. Like a dozen others within four shots of the lead, he’ll have to begin that process of confronting failure all over again Sunday. On this course in particular, it’s essential to access in advance how much mortification is simply part of the price of a U.S. Open prize.

Perhaps there has never been a confidence-shredding U.S. Open course that has been so viciously set up to play on exactly this natural human tendency to quit too soon. The first six holes at the Olympic Club are probably the toughest opening stretch in the event’s history. On Thursday, five of them ranked first, second, third, fifth and sixth in difficulty on the course.

Almost as bad, there is only one birdie hole (No. 7) until you get to the 15th tee. Oh, the last mile is (relatively) a piece of cake with the 108-yard 15th hole, the back-to-back par-5 16th and 17th holes and a tiny, tricky, 344-yard 18th hole. But how many contenders will arrive there with their sanity, and their mathematical chances, still intact? After taking such a beating for so long for such high stakes, how many players can switch to attack mode?

In other words, that fine line between 67-68 and 75-76 is perilously real. But it is likely to be the middle of that range which proves most important.

Here is a partial list of players, within the last six years, who could have won outright, or gotten into a playoff, if they had simply carded an even-par round on the last day of this event: Tiger Woods (twice), Lee Westwood, Phil Mickelson (2 over would have won at Winged Foot), Bubba Watson (3 over would have won at Oakmont), Vijay Singh, Ernie Els, Gregory Havret, Steve Stricker, Colin Montgomery, Paul Casey, Justin Rose, Stephen Ames, Kenneth Ferrie and Ricky Barnes (3 over would have won).

Perhaps most painful was Dustin Johnson, who needed a 5-over 76 to win the 2010 U.S. Open but lost hope too soon and shot 82.

Of course, shooting par on Sunday is tough. But not that tough. Doing it over four days? Now that’s rough. But the number of players who have semi-given up on themselves in the final round, when 1 or 2 or (gack) 5 over might still win, is a long, familiar U.S. Open theme.

Yes, Sunday at the U.S. Open — the ultimate head-game afternoon in all of sports — is now upon us again. Find your favorite chair and, as some hero with gifts we’ll never imagine slumps his shoulders, practice your most malevolent, scare-the-kiddies laugh: “Bwaaaahahahaha.”

What an ideal leader board we have for such a test. Give an edge to the veterans who’ve learned, often from bitter U.S. Open experience, that “never quit” is the swing thought that counts the most in America’s championship.

At 42, Furyk epitomizes the player who uses his experience, his knowledge of the course and weather conditions, to estimate a target score that could win. Is that smart strategy or a snare and a delusion?

“A little of both,” he said, chuckling. “I tend to pick too low [a winning score. Jack] Nicklaus made that popular, but he always seemed to pick the right number. . . . I won’t try to look at leader boards too much.”

Usually, the U.S. Open just won’t let you know, even in mid-round, what will be necessary to win it. But there are plenty of quality names capable of charging at the leaders, including Lee Westwood, 39, desperate to win his first major, and two-time U.S. Open winner Ernie Els, 42, who still has the game to win if his notorious nerves don’t fail him.

If you want to dream about the final-round 66 that almost never happens at America’s championship, then you can include so many juicy names your head will swim with possibilities — from red-hot rumpled Jason Dufner to edge-of-fantasy 17-year-old amateur Beau Hossler, a Los Angeles area high school player who missed the cut last year at Congressional but is now part of a six-way tie for eighth place, four shots behind.

Who is one shot behind that teenager? Why it’s Tiger Woods, whose 75 was five shots worse than playing partner Furyk and included few shots, or decisions, of distinction and a shaky, timid putter, too.

Unfortunately for all of those named above — save one man who’ll stand alone at sundown — a swimming head is exactly what U.S. Open Sunday always produces. At the Masters, you know what you need to do: Get through Amen Corner in one piece, then make as many birdies as possible, and maybe an eagle, as you stampede to the clubhouse.

But at the U.S. Open, with its 18 separate torments, it’s almost impossible to function properly if you fall into the trap of thinking about anything, anything at all, except your next shot.

In almost every other golf event, if you aren’t actually the 54-hole leader, you’re conditioned to believe that “a score in the 60s” is absolutely essential to victory. Even if the thought is not conscious, even if it’s suppressed, the impulse to “go low” is part of an elite pro’s DNA. That impulse will work against every chaser, even if they know better.

If you’re in the lead, like McDowell and Furyk, then the first bogey or two of the final round on those early holes can seem like the end of your world. Surely that tough, proven fellow playing with you, already the owner of a U.S. Open title, won’t crack. That’s how 75-76s are born.

Don’t think big thoughts. Don’t feel large emotions. Play the next shot. It’s so easy to say. Yet, decade after decade on Sunday at the U.S. Open, it’s almost impossible to do. That’s why we can’t take our morbidly fascinated eyes off golf’s most wrenching spectacle.

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